.sup.90 Y is a pure .beta. radioactive nuclide which has high energy (Emax=2.28 MeV) and short half-life (T1/2=64 hours). Owing to the excellent nuclear characters, .sup.90 Y is so far the most popular radioactive nuclide for the therapy and application in nuclear medicine field. However, the half-life of .sup.90 Y is too short to be stored in a product form, so it is more practical for producing .sup.90 Y by a generator which generates .sup.90 Y when it is required.
A conventional method for generating .sup.90 Y from .sup.90 Sr includes steps of converting .sup.90 St into .sup.90 Y and then separating .sup.90 Y from .sup.90 Sr by solvent extraction. Solvent extraction has disadvantages of production of organic wastes and great amount of reagent consumption.
An ion-exchange method can also be used for generating .sup.90 Y from .sup.90 Sr. By this method, .sup.90 Y is obtained through column chromatography which is a simpler process that the solvent extraction method. In the past, several ion-exchange systems have been used in this field, for example, a citrate, lactate, oxalate, acetate or EDTA system. However, the required column for effectively separating .sup.90 Y from .sup.90 Sr is quite long and thus the required amount of the elutant is also large. Accordingly, the cost will be too high. There is also an isotope-exchange method used for generating .sup.90 Y from .sup.90 Sr, but it is unsuitable for being repeatedly used. Of course, some new ion-exchange methods are developed or being developing now.